Wednesday, June 11, 2014

Anacortes










A new beach (several, actually) and a very small pocket estuary. An amazing contrast to the remains of the old Custom Plywood mill. And probably quite a contrast to whatever marsh or beach marked this shoreline before the 1860s.

Here are two previous entries on this site:

AERIAL VIEW (probably out of date)

These beach projects often rearrange themselves very rapidly after construction. After all, they involve placing loose sediment in places where waves and tidal currents are expected to move it around. This isn't necessarily a problem - good projects are designed to allow this kind of adjustment. But often these early changes are not well documented and as a result, we lose an opportunity to learn and to improve future projects. There will be some sort of formal monitoring of this site, but these programs often miss some of the most important (and often most interesting) geomorphic details.

On a brief, late afternoon visit, here's what caught my eye:

  • A new flood tide delta was building inside the southern edge of the inlet, shifting gravel from the beachface into the lagoon.
  • A mid-tide berm was building northward across the outlet channel, pushing it northward.
  • The sandy crest of the outer spit was eroding on both sides, although more on the south. I wonder if this sandy material - and the beach grass - will make it through next winter.
  • The beach to the north was looking pretty cool, but I didn't have time to explore further.



Possession









This small, unadvertised state park at the southern tip of Whidbey is a great place for an early morning walk on the beach below Possession Head, a tall landslide prone bluff that faces south down the Sound.  Wave action erodes the bluff, carrying sediment northward up the southeast side of the island, past this state park, the county boat ramp, and the Glendale pier. Later it sneaks under the Clinton ferry dock, along Brighton Beach, and eventually to Sandy Point.  Much of the sediment probably never makes it, getting detoured to the bottom of Puget Sound by the steep offshore slope, which in some places is not far from shore at all.


The old house at the park is built on what appears to be fill at the mouth of a steep ravine.  The shoreline had been held together by an old timber pile bulkhead for many decades, but by 2004 when I first saw it, it was in serious disrepair. There was discussion of replacing it, but a few years ago the old wall was removed, the bank regraded and planted, and some of the large wood rearranged.  I wondered how this site would behave - fill usually erodes rapidly and this site is exposed to strong oblique waves from the south.  But it looks like it is doing just fine without the wall.  There is some continuing erosion, but not much.


Rounding the corner from one of these south-facing headlands, we often encounter local complications in the beaches.  Small spit-like accretional features are common. Basically, the beach can't turn the corner that fast and it overshoots before gradually reconnecting with the drift-aligned shoreline farther north (in reality it is a little bit more complicated than this).  There's another neat example just a few miles west at Maple Point.

AERIAL VIEW

Here, there is a small accretional bulge right in front of the site and bank erosion is reduced as a result. Thus the success of the bulkhead removal. Sure it would be great if you could apply general principles and regional assessments to beach projects, but in the end, it's all local.

Despite the wide place in the berm, the beach itself is incredibly narrow here. In one spot along here, a good spring low tide will actually expose the edge of the platform - which is abrupt and plunges into several hundred feet of water. I'll come back at one of those tides someday and then post a picture.